Presently, data cartridge libraries are primarily used to archive data, i.e., store data that is not immediately needed by the host computer, and provide archived data to the host computer when the data is needed. To elaborate, the typical data cartridge library receives data from a host computer and causes the data to be stored or recorded on the recording medium located in one or more data cartridges. When the host computer requires some of the data that was previously stored in a data cartridge, a request for the data is sent from the host computer to the library. In response, the library identifies the data cartridge(s) in which the desired data is located, retrieves the data from the recording medium within the cartridge(s), and transmits the retrieved data to the host computer system.
Presently, most data cartridge libraries are comprised of: (a) a plurality of storage slots for holding data cartridges with the slots being in fixed locations during operation of the library; (b) one or more drives that are each capable of writing data onto the recording medium located in a data cartridge and/or reading data from the recording medium located in a data cartridge; (c) a cartridge picker device that is capable of moving individual data cartridges between the slots and the drives; and (d) an interface for receiving data from and transmitting data to a host computer. Such libraries are considered to be “cartridge based” data cartridge libraries (hereinafter referred to as cartridge-based libraries) because, during operation of the library, the movement of cartridges to and from the fixed storage slots is accomplished solely by a cartridge picker device that transports individual cartridges. Generally, the operation of a “cartridge-based” library involves using the cartridge picker device: (a) to move a cartridge from a fixed storage slot to a drive so that data can be either written on to or read from the recording medium in a cartridge; and (b) to move a cartridge from a drive to a storage slot.
One approach to implementing storage slots in a “cartridge-based” library is to create a wall with a number of fixed slots. This approach has a distinct drawback when adding cartridges to the library and removing cartridges from the library. Namely, the fixed slots require the cartridges to be loaded into the slots one at a time and removed from the slots one at a time. This drawback is particularly acute in situations in which a library has a large number of slots and a large number of cartridges either needed to be inserted into or removed from the slots. An example of such as situation is when the library is being initially populated with cartridges. In such situations, an operator typically powers down the library and inserts the cartridges into the slots by hand. Another approach to the implementation of storage slots in a “cartridge-based” library involves the use of a data cartridge magazine that an operator can mount or demount from a wall in the library. Typically, the magazine is a box-like structure that has an open side through which cartridges can be inserted into and removed from the magazine, a partitioning structure that defines a number of slots for holding data cartridges, and a mounting structure that allows the magazine to be mounted and demounted from a wall in the library. A significant advantage of the magazine approach is that an operator, by manipulating magazines rather than individual cartridges, is able to more quickly insert a large number of cartridges into a library and more quickly remove a large number of cartridges from a library. However, regardless of whether cartridges are being inserted into or removed from the library, the operator is still typically required to powerdown the library or otherwise disable the cartridge picker device to avoid being injured by the device during the mounting or de-mounting of a magazine.
In many instances, only one data cartridge needs to be either inserted into or extracted from a “cartridge-based” library. In these instances, the powering down of the library or disabling of the cartridge picker device so that an operator can insert or extract the cartridge is undesirable. To address this situation, many “cartridge-based” libraries employ an entry/exit port that allows an operator to insert a single data cartridge into the library and extract a single data cartridge from the library without being exposed to the cartridge picker device. Because the operator is not exposed to the cartridge picker device, the library does not need to be powered down or the cartridge picker device disabled during the insertion or removal operation. Generally, the entry/exit port is comprised of a slot for holding a data cartridge and a device that places the slot in one of two states. In the first state, the slot of the entry port is exposed to the environment exterior to the library such that an operator can access the slot. When the slot is in the first state, the exit/entry port substantially prevents an operator from accessing the interior of the library by way of the slot and, as a consequence, prevents the operator from being exposed to injury by the cartridge picker device. In the second state, the slot of the entry/exit port is exposed to the interior of the library such that the cartridge picker device is able to access the slot. When the slot is in the second state, the entry/exit port prevents an operator from accessing the interior of the library via the slot. For the insertion of a data cartridge into the library, the slot is placed in the first state and the operator inserts a data cartridge into the slot. The slot is then placed in the second state to make the cartridge available to the cartridge picker device for placement elsewhere in the library. For the extraction of a data cartridge, the slot is placed in the second state and the cartridge picker device places a cartridge in the slot. The slot is then placed in the first state to make the cartridge available to an operator for removal.
Entry/exit ports that provide the ability to insert multiple data cartridges en masse into a library and extract multiple data cartridges en masse from a library are also known. Such exit/entry ports are typically employed in libraries that have a relatively high number of slots and are used in a manner in which the insertion and/or extraction of several cartridges at a time is desirable but the powering down or disabling of the cartridge picker device to allow a manual insertion/extraction of the cartridges is undesirable. For these types of libraries, the operator is effectively limited to inserting and extracting data cartridges via the entry/exit port. To provide the operator with the ability to insert or extract several cartridges at a time, the entry/exit port has multiple slots that form a fixed part of the port. Alternatively, an entry/exit port is provided that allows a magazine with multiple slots to be inserted into the port by the operator. With respect to this type of entry/exit port, insertion of multiple cartridges into the library is accomplished by placing the port in a first state so that an operator can either: (a) populate a magazine that is already present in the port with multiple cartridges, or (b) place a magazine and accompanying cartridges into the port. The port is then placed in a second state so that the cartridge picker device can individually move each of the cartridges in the magazine to other locations within the library. To extract multiple cartridges, the port is placed in the second state and the cartridge picker device individually moves cartridges from various locations in the library to the magazine. After all of the cartridges that are to be extracted have been placed in the magazine, the port is placed in the first state. Once in the first state, an operator can either individually remove cartridges from the magazine or remove the magazine from the port.
In many applications, the user of a cartridge-based library has a current need for a library with a particular data cartridge storage capacity and/or a particular number of drives but anticipates that there will be a future need for a library with a greater data cartridge capacity and/or greater number of drives. To address this situation, cartridge-based libraries have been developed that allow the user to initially acquire a library that satisfies the current needs and when future needs exceed the data cartridge and/or drive capacity of the library, allow the user to expand the library. Certain cartridge-based libraries that have this expansion capability expand the library with a unit or units that expand the library horizontally. Other cartridge-based libraries expand the library in a vertical fashion. In either case, such cartridge based libraries are in many cases able to pass cartridges between the original library and the expansion units by expanding the cartridge picker system.
In certain cartridge-based libraries, the use of expansion units that provide greater data cartridge storage capacity and/or a greater number of drives and an expandable cartridge picker system is not practicable. For instance, the use of expansion units and an expandable cartridge picker system is typically not practicable for libraries that employ a cartridge picker system that traverses a circular path, which are sometimes referred to as “silo” libraries. Nonetheless, in many situations, there is a need to transfer cartridges between libraries for which the expansion approach is impracticable and to do so automatically, rather than transfer a cartridge out of one library by its entry/exit port and then have an operator transfer the cartridge to the entry/exit port of the other library. Consequently, cartridge pass-through ports have been developed that allow one library to automatically transfer a cartridge to another library, i.e., without operator assistance.